The influence of CO2, SOx, NOx and soot dust on the productivity of microalgae was considered using Nannochloropsis salina and Phaeodactylum tricornutum. Microalgae are viewed as a possible means of combeting global warming. These microalgae can be easily cultivated in a high CO2 gas concentration of 15 vol%. SO2 gas itself does not influence the growth of microalgae. However, when the SO2 concentration is high, the pH of the medium decreases and the productivity of the microalgae is Lowered. The presence of NO does not influence the growth of microalgae. NO absorbed in the medium is changed to NO2- and utilized as a nitrogen source. As for Ni and V contained in soot dust, when the dissolved concentrations of these metals in the medium exceed more than 1 and 0.1 ppm, respectively, the microalgae productivity decreases, however, under actual conditions, their concentrations are normally lower than these values. The above results obtained in a small scale test using a simulated gas were confirmed in a field test using a raceway-type reactor with actual flue gas.